Improve remarkup performance (Phabricator)

Summary: As we've moved more remarkup logic post-cache (e.g., to implement policy-aware rules), we're paying more of a price for it. Improve performance in Phabricator by sharing engine instances where possible.

Test Plan: With next diff, this drops 75% of the cost of markup handling in Conpherence.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D5510

src/applications/transactions/storage/PhabricatorApplicationTransactionComment.php

@@ -61,7 +61,7 @@ abstract class PhabricatorApplicationTransactionComment
 
 
   public function newMarkupEngine($field) {
-    return PhabricatorMarkupEngine::newMarkupEngine(array());
+    return PhabricatorMarkupEngine::getEngine();
   }
 
 

src/infrastructure/markup/PhabricatorMarkupEngine.php

@@ -337,6 +337,27 @@ final class PhabricatorMarkupEngine {
     return self::newMarkupEngine($options);
   }
 
+  /**
+   * @task engine
+   */
+  public static function getEngine($ruleset = 'default') {
+    static $engines = array();
+    if (isset($engines[$ruleset])) {
+      return $engines[$ruleset];
+    }
+
+    $engine = null;
+    switch ($ruleset) {
+      case 'default':
+        $engine = self::newMarkupEngine(array());
+        break;
+      default:
+        throw new Exception("Unknown engine ruleset: {$ruleset}!");
+    }
+
+    $engines[$ruleset] = $engine;
+    return $engine;
+  }
 
   /**
    * @task engine